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package uni.j2ee.forum.ejb.impl;

import java.beans.Expression;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.annotation.Resource;
import javax.ejb.EJBException;
import javax.ejb.TransactionManagement;
import javax.ejb.TransactionManagementType;
import javax.persistence.EntityManager;
import javax.persistence.Query;
import javax.persistence.TypedQuery;
import javax.transaction.UserTransaction;

/**
 *
 * @author ivan
 */
@TransactionManagement(TransactionManagementType.BEAN)
public abstract class AbstractFacade<T> {
    @Resource
    UserTransaction transaction;
    
    private Class<T> entityClass;

    public AbstractFacade(Class<T> entityClass) {
        this.entityClass = entityClass;
    }
    
    

    protected abstract EntityManager getEntityManager();

    public void create(T entity) {   
         try {
            try {
                transaction.begin();
                 getEntityManager().persist(entity);
           } finally {
                transaction.commit();
           }
        } catch (Exception e) {
          Logger.getLogger(ForumPostFacade.class.getName())
                   .log(Level.SEVERE, "could not create entity: " + entity, e);
           throw new EJBException(e);
        }
    }

    public void edit(T entity) {
        getEntityManager().merge(entity);
    }

    public void remove(T entity) {
         try {
            try {
                transaction.begin();
                 getEntityManager().remove(getEntityManager().merge(entity));
           } finally {
                transaction.commit();
           }
        } catch (Exception e) {
          Logger.getLogger(ForumPostFacade.class.getName())
                   .log(Level.SEVERE, "could not create entity: " + entity, e);
           throw new EJBException(e);
        }
    }

    public T find(Object id) {
        return getEntityManager().find(entityClass, id);
    }

    public List<T> findAll() {
        javax.persistence.criteria.CriteriaQuery cq = getEntityManager().getCriteriaBuilder().createQuery();
        cq.select(cq.from(entityClass));
        return getEntityManager().createQuery(cq).getResultList();
    }

    public List<T> findRange(int[] range) {
        javax.persistence.criteria.CriteriaQuery cq = getEntityManager().getCriteriaBuilder().createQuery();
        cq.select(cq.from(entityClass));
        javax.persistence.Query q = getEntityManager().createQuery(cq);
        q.setMaxResults(range[1] - range[0]);
        q.setFirstResult(range[0]);
        return q.getResultList();
    }
    
      public int count() {
        javax.persistence.criteria.CriteriaQuery cq = getEntityManager().getCriteriaBuilder().createQuery();
        javax.persistence.criteria.Root<T> rt = cq.from(entityClass);
        cq.select(getEntityManager().getCriteriaBuilder().count(rt));
        javax.persistence.Query q = getEntityManager().createQuery(cq);
        return ((Long) q.getSingleResult()).intValue();
    }
    
}
